According to the recent trend, a radio communication system has an increased service frequency band, and cells having decreased radiuses for high speed data communications and increased telephone traffic. This may cause many problems when applying the existing centralized cellular radio network method as it is. More concretely, a configuration of a radio link has a degraded flexibility due to a fixed location of a base station. This may cause a difficulty in providing efficient communication services in a radio environment where traffic distributions or requested telephone traffic are severely changed.
In order to solve these problems, the next generation radio communication system referred to as LTE-Advanced (Long Term Evolution Advanced) system or E-UTRA (Evolved Universal Terrestrial Radio Access) considers a Multi-Hop relay system. This multi-hop relay system has the following advantages. Firstly, a cell service area may be increased by covering partial shadow areas occurring inside a cell area, and a system capacity may be increased. Furthermore, an initial situation requiring less service is implemented by using a relay. This may reduce the initial installation costs.
In the relay system, a communication channel between a base station and a terminal may be implemented through a direct connection therebetween, or may be implemented in the form of a relay node (RN). Here, the communication channel formed between the base station and the RN is called ‘backhaul’ link.
A communication method through the backhaul link channel may be categorized into an ‘in-band backhaul’ method and an ‘out-band backhaul’ method. The in-band backhaul method indicates a method for dynamically sharing frequency resources between a backhaul communication and a terminal communication. On the other hand, the out-band backhaul method indicates a method for separately using frequency resources between a backhaul communication and a terminal communication.
When transmitting a backhaul signal through a backhaul link, propagation delay occurs according to a communication environment, etc. Since a backhaul signal transmitted through a backhaul link is generally designed with consideration of propagation delay, available resources of a backhaul link channel may not be fixed but variable according to a communication environment.
More concretely, in a communication environment where propagation delay is great, the amount of resources available as a backhaul signal is reduced. On the other hand, in a communication environment where propagation delay is less, the amount of resources available as a backhaul signal is increased.
In this case, a reference signal included in the backhaul signal needs to be designed so as to be changeable according to the amount of the resources available as the backhaul signal.